The present invention relates to a color image recording apparatus. More particularly, the present invention relates to an inexpensive and compact color image recording apparatus of simple configuration that employs a laser light source capable of simultaneous emission of laser beams associated with exposure to red, green and blue light.
Conventional color image recording apparatuses adopt "digital exposure" in which an digital electric signal carrying image information is converted to a light beam which is deflected to expose a light sensitive material and other various recording materials. While various techniques are available to effect "digital exposure", exposure to a laser beam finds extensive use for such advantages as uniformity and high-speed performance.
FIG. 7 is a schematic representation of a color image recording apparatus that adopts the technique of exposure to a laser beam. The color image recording apparatus generally indicated by 300 in FIG. 7 has three laser light sources 302R, 302G and 302B that are associated with exposure to red (R), green (G) and blue (B) light. The laser beams emitted from the respective light sources are shaped with associated collimator lenses 304R, 304G and 304B, then launched respectively into a reflecting mirror 306R and dichroic mirrors 306G and 306B, from which they are reflected and have their optical axes aligned with one another to form a single beam.
The Resulting single laser beam is launched into a light deflector such as a polygonal mirror 308 to be reflected and deflected in the main scanning direction. The deflected beam passes through an f.theta. lens 310 and is bent down by means of a cylindrical mirror 312 to be focused for scanning and exposure of a recording material A that is being transported with two roller pairs 314 and 316 in the sub-scanning direction indicated by arrow Z which is generally perpendicular to the main scanning direction.
As described above, the color image recording apparatus 300 employs three laser light sources that emit at wavelengths associated with exposure to R, G and B light, with the optical axes of the issuing laser beams being brought into alignment with one another to produce a single laser beam that scans for exposing the recording material A being transported in the sub-scanning direction. In order to align the optical axes of the respective beams from the three laser light sources, not only the reflecting mirror 306R but also the dichroic mirrors 306G and 306B are necessary and this causes the disadvantage of increasing the size and cost of the apparatus 300. Further, the need for bringing the optical axes of the three laser beams into accurate alignment with one another introduces difficulty in adjusting the optical system.
Instead of aligning the optical axes of the respective laser beams associated with exposure to R, G and B light, the exit angles of these laser beams may be so adjusted that they fall at substantially the same point on the recording material A. Various apparatuses have been proposed for recording images by this principle. These apparatuses have the advantage of obviating the need for providing dichroic mirrors and other members to bring the optical axes of three laser beams into alignment, but on the other hand, the laser beams fall at different positions on the light deflector such as a polygonal mirror, with consequent increase in the size and cost of the latter. Further, great difficulty is involved in adjusting the laser beams to fall at the same position on the recording material A.
In either type of the image recording apparatus described above, semiconductor lasers or gas lasers are commonly used as the laser light sources. Gas lasers are not only expensive but also large in size, so they have the disadvantage of increasing the size and cost of the recording apparatus itself. On the other hand, semiconductor lasers are compact and inexpensive but none of the semiconductor lasers available today are capable of emitting laser light at wavelengths in the visible range that are associated with exposure to G and B light. Thus, common recording materials having a spectral sensitivity in the visible range are not usable with semiconductor lasers and instead, special recording materials having a spectral sensitivity in the infrared region must be employed. If one wants to use common recording materials having a spectral sensitivity in the visible range, laser beams must be modulated with a special wavelength converting device such as a second harmonic generator (SHG) but then, the resulting increase in the number of components renders the recording apparatus not only expensive but also bulky.
Japanese Laid-open Patent Application No. 279314/1987 describes a recording apparatus that uses a white light emitting laser, with the emitted laser beams being modulated with an accoustooptical modulator (AOM) at the wavelengths that are associated with exposure to R, G and B light. However, the AOM used in this apparatus is quite expensive and a complex, drive circuit is necessary to control the wavelength-associated modulation with the AOM. As a result, the recording apparatus proposed by said patent application has the disadvantage that it involves both complicated control and high cost.